1. Field of the Invention
The invention relates to a looper drive mechanism of a sewing machine, and particularly to a looper drive mechanism for transmitting rotation of a main shaft to a looper.
2. Description of the Background Art
Generally, an overlock machine is provided with one or two loopers, which carry out elliptical or circular motion perpendicular to a path of a linear motion of a needle. The looper is driven by a looper drive shaft, which is perpendicular to a main shaft and is oscillated by a main shaft (drive shaft) of the sewing machine through motion conversion/transmission means such as an eccentric cam, spherical cam and bevel gear. For example, in a looper drive mechanism shown in FIG. 6, a main shaft 100 is provided with a crank 102 to which a link 103 is connected, and a looper drive shaft 104 is connected to the link 103 through an arm 105 and a spherical coupling arm 106. As the main shaft 100 rotates, the link 103 vertically moves, whereby the arm 105 is swung or oscillated to rotate the looper drive shaft 104, which, in turn, oscillates an oscillating arm 107 to drive a looper 108.
However, in the structure employing the spherical cam and spherical arm, manufacturing of the spherical arm itself is difficult and expensive, so that the whole structure becomes expensive.
On the other hand, in the looper drive mechanism employing the eccentric cam, the eccentric cam rotates together with the main shaft and the rotary motion of the eccentric cam caused by the rotation of the main shaft is transmitted through a connecting rod and a spherical arm to the looper drive shaft for driving the looper. In this case, it is necessary to slide the connecting rod relative to the eccentric cam, so that high accuracy cannot be obtained in the motion of the looper, and thus a good seams cannot be obtained. In the structure employing the bevel gear (disclosed, e.g., in the Japanese Laid-Open Patent Publication No. 53-23755 (1978)), the rotary motion of the main shaft, the motion of which is converted by the bevel gear must be further converted by the spur gear, crank, link or the like into the oscillatory motion of the looper drive shaft. This results in a disadvantage that the structures are complicated, the number of parts is large, the assembly and manufacturing are laborious, and consequently the construction is expensive.
In order to solve the disadvantages of the looper drive mechanism in the prior art, there has been proposed a looper drive mechanism employing a groove cam (Japanese Laid-Open Patent Publication No. 62-176487 (1987)). In this looper drive mechanism, as shown in FIG. 7, a coned dram cam 201 provided with grooves 201a and 201b is attached to a main shaft 200. When the coned dram cam 201 rotates together with the main shaft 200, the oscillation of support arms 204 and 205 for rollers 203a and 203b engaging the grooves 201a and 201b are restricted by the grooves 201a and 201b while the looper drive shafts 206 and 207 are oscillated. This looper drive mechanism requires less number of parts, as compared with the above described looper drive mechanism, and, once a machine for manufacturing the hourglass cam 201 is manufactured, an accurate looper driving operation will be carried out with a simple mechanism.
These looper drive mechanisms in the prior art, however, have such a disadvantage that the assembling operation is time-consuming and laborious, in addition to the respective disadvantages described above. Specifically, in the manufacturing of these looper drive mechanisms, it is necessary to sequentially assemble the cam or gear, looper drive shaft and looper with the main shaft, so that manufacturing steps are complicated, and thus are time-consuming and laborious.
The present invention has been developed in view of these disadvantages of the looper drive mechanisms in the prior art, and it is an object of the invention to provide a looper drive mechanism, in which the number of parts is small, the manufacturing is easy and the accuracy is high.